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• Non-repudiation: is the entity’s ability to assume responsibility for its actions on

its data set and not to refuse its procedures, so that the service level agreement

between the two parties is confirmed without any denial, and its consequences if

it does not apply, significant material losses, in addition to the loss of confidence

and reputation [21].

• Authenticity: This means that the information in the cloud provider is original data

so that the owner and origin of the data can be ascertained, and this is accomplished

by numerous signature schemes [4].

• Reliability: is the ability to deliver results consistently.

There are some other requirements for achieving security, such as: physical secu-

rity, data sanitization, non-collusion resistance, data segmentation, data traceability

and labeling, data location restrictions, backup procedures, authentication. Table 1

gives us the outline of cloud computing security issues.

2.6

Security in the SPI Model

As we mentioned, the cloud consists of three layers, which are SaaS, PaaS, and IaaS,

so each provider has its own infrastructure, platform, and software layer [23]. Thus,

when the customer deals with the applications provided by the cloud service provider,

he is forced to use the infrastructure and platform that that provider provides. Any

breach or attack in IaaS will necessarily affect the security of the other two layers

and vice versa, therefore, the cloud service provider has full access to customer data

and knowledge of their location [24], which determines the level of abstraction of

each layer and the extent of user control, so IaaS has greater control over the client,

and control is decreasing towards the upper layers, which increases the security risks

in them and vice versa.

Of course, each cloud service model has its own security weaknesses in addition

to the presence of common obstacles that have an impact on all of them [25], and this

increases the security dependency among them [6], we will talk about that below.

2.6.1

Software-as-a-Service (SaaS) Security Issues

As mentioned, SaaS provides application services such as email, conference

programs, and other applications [26]. The users of this layer have less control over

security than other layers, so the security concerns about this layer are rather large.

The geographical location of the customer information site is a concern, in addition to

that the information is processed and stored in this layer as normal text and therefore

must be encrypted to maintain its confidentiality [26], backup storage concerns [27],

in addition to that some cloud providers provide users with the ability to jointly access

data storage locations (Multiple Leasing Service), therefore CSP must separate any

user’s data from other unauthorized users. Sometimes a CSP causes a violation of